The present invention relates to a switching network of the type in which at least four junctions are connected with each other in an annular arrangement by means of disconnectable current branches.
A switching network, or switchgear of this type is known for example from an article by B. Stepinski entitled "Novel Aspects of the Construction of Outdoor Switchgear Installations to 765 kv" in Brown Boveri Mitt. 65, 1978 (4), 268 ff. In this installation breaker units are provided; in the current branches connecting the junctions they consist generally of a series circuit of a first disconnecting switch, a power switch, an instrument transformer and a second disconnecting switch. If, in such an installation, a bus bar system or a breaker unit should fail, the supply of power is maintained, as the unaffected junctions of the installation remain interconnected in spite of the disconnection of the affected part of the system.
The safety of the power supply is receiving rising priorities. It is therefore necessary to provide switchgear installations which assure optimum availability and reliability. Thus, for example, A. Klimann proposed in Electrical World, Aug. 15, 1979, page 60 ff, a switchgear installation with a high degree of redundance. In this switchgear, the breakers are connected in the form of "pyramids". This switchgear exhibits an improved degree of safety with respect to the annular arrangement, but a very high number of disconnecting switches, for example 10 power and 33 disconnecting switches in a substation with six fields, involving high space requirements and increased costs.
It is therefore the object of the invention to further develop a switchgear of the aforementioned generic type so that its redundance will be improved substantially at a low expenditure for equipment and with reduced space requirements.
The object of the invention is attained by dividing the network into at least two groups each containing at least two junctions, and connecting each junction in one group with each junction in another group by means of a bridging branch containing a common load switch and disconnecting switches respectively connected between one terminal of the load switch and one of the junctions in each of the two groups. The switchgear installation according to the invention is characterized by high reliability and availability values, without the need for large investments in equipment. As each junction may be connected through three parallel switching points with the rest of the annular system, in case of the failure of a switching point, two further switching points remain, through which the connection of the junction affected by the failure of the switching point with the rest of the annular system is assured. Should then another of the two aforementioned switching points fail, the supply of the affected junction is assured by the functional security of the third switching point.
Examples of the invention are represented hereinbelow with the aid of the drawings in a simplified form.